1. Field of the Invention
The invention relates to a transmission system for transmitting packets which comprise an information word group and a control word group (header), the control word group comprising an identification of the packet type such as an identification of the virtual transmission channel and/or of the group of virtual transmission channels via which the packet is being transmitted, which transmission system comprises access control means for granting or refusing said packets access to the part of the transmission system situated downstream of the access control means, depending on the incoming volume of packets.
2. Prior Art
Within the field of ATM (Asynchronous Transfer Mode), such a transmission system is generally known. Inter alia, such a transmission system has been described in the reference mentioned under C.
In the known transmission systems of the abovementioned type, packets (data cells) are therefore admitted, or not admitted, to the downstream part of the transmission system on the basis of, for example, the mean arrival frequency of said packets or on the basis of another criterion. Preferably, the transmission of packets per transmission channel (or group of channels) is monitored, a certain limit therefore being imposed per transmission channel (or group) on the number of packets which, for example, are transmitted per unit of time to the downstream system. A drawback of the known transmission systems is that, as soon as the number of packets (for example of a particular sort, a particular channel) becomes too large, the packets are discarded. Said discarding of said packets is, however, entirely to be approved since (normally) it could have been prevented by the provider of the packets, the user of the relevant transmission channel: the user must not, for example, exceed a particular maximum frequency, on pain of losing packets. A drawback of the known transmission systems of the type mentioned is, however, that there is in fact no control at all on the discarding of packets. The transgression of the maximum permitted packet input frequency may in fact be the consequence either of a deliberate attempt by the user to transmit more packets per unit time than he is permitted or of a lack of checking on his part on the possible transgression of the maximum. It may also be important to know if a transgression is occasional and of little significance or is frequent and appreciable. Especially if the transgression is appreciable and prolonged, there is a very real ,chance that the transgression is the consequence of a technical fault in the user's equipment or in the equipment of the transmission system manager.